It's an excellent idea, because if the font fails to load you get an actual human-readable fallback, instead of "whatever some random other font put in the PUA". For example, whenever I visit GitHub I find the interface decorated with random Korean glyphs and 7-segment-LCD symbols, which is somewhat distracting and confusing. With a ligature system like this, I'd see things like "file" and "folder" which at least make sense.